The present invention relates to systems for more accurately controlling the placement of implant materials percutaneously or otherwise under pressurized flow. Procedures for such placement include procedures for the repair of hard tissue by injection of hard tissue implant materials, such as in hip augmentation, mandible augmentation, and particularly vertebroplasty, among others. Procedures also include the placement of implant materials in soft tissues.
Polymethylmethacrylate (PMMA) has been used in anterior and posterior stabilization of the spine for metastatic disease, as described by Sundaresan et al., xe2x80x9cTreatment of neoplastic epidural cord compression by vertebral body resection and stabilization.xe2x80x9d J Neurosurg 1985;63:676-684; Harrington, xe2x80x9cAnterior decompression and stabilization of the spine as a treatment for vertebral collapse and spinal cord compression from metastatic malignancy.xe2x80x9d Clinical Orthodpaedics and Related Research 1988;233:177-197; and Cybulski, xe2x80x9cMethods of surgical stabilization for metastatic disease of the spine.xe2x80x9d Neurosurgery 1989;25:240-252.
Deramond et al., xe2x80x9cPercutaneous vertebroplasty with methyl-methacrylate: technique, method, results [abstract].xe2x80x9d Radiology 1990;117(suppl):352; among others, have described the percutaneous injection of PMMA into vertebral compression fractures by the transpedicular or paravertebral approach under CT and/or fluoroscopic guidance. Percutaneous vertebroplasty is desirable from the standpoint that it is minimally invasive, compared to the alternative of surgically exposing the hard tissue site to be supplemented with PMMA or other filler.
A general procedure for performing percutaneous vertebroplasty involves placing a cannula with an internal stylet into the desired implantation site. The cannula and stylet are used in conjunction to pierce the cutaneous layers of a patient above the hard tissue to be supplemented, then to penetrate the hard cortical bone of the vertebra, and finally to traverse into the softer cancellous bone underlying the cortical bone. Once positioned in the cancellous bone, the stylet is then removed leaving the cannula in the appropriate position for delivery of a hard tissue implant material to reinforce and solidify the damaged hard tissue.
A syringe is next loaded with polymethyl methacrylate (PMMA) and connected to the end of the cannula that is external of the patient""s body. Pressure is applied to the plunger of the syringe to deliver the PMMA to the site of damaged bone at the distal end of the cannula. Because in general, 10 cc syringes are only capable of generating pressures of about 100-150 psi, this places a limitation on the viscosity of the PMMA that can be effectively xe2x80x9cpushed throughxe2x80x9d the syringe and cannula and fully delivered to the implant site. Of course, the use of a small barrel syringe, e.g., a 1 cc syringe enables the user to generate higher driving pressures. For example pressures of 800 psi and possibly as high as 1000-1200 psi (depending upon the strength of the user and the technique) may be generated using a 1 cc syringe. A serious limitation with the use of a 1 cc syringe, however, is that it will not hold a large enough volume to complete the procedure in one step or xe2x80x9cloadxe2x80x9d and must be reloaded several times to complete the procedure, since, on average, about 3.5 cc of implant material per side of the vertebral body are required for an implantation procedure. This makes the procedure more complicated with more steps, and more risky in that the polymerization of the implant material causes it to become increasingly more viscous during the additional time required for reloading. Another problem with a 1 cc syringe is lack of control, as high pressures are generated in a xe2x80x9cspike -likexe2x80x9d response time and are not continuously controllable.
A viscous or syrupy consistency of PMMA is generally believed to be most advantageous for performing percutaneous vertebroplasty. Such a consistency insures that the implant material stays in place much better than a less viscous, more liquid material. Additionally, when PMMA is implanted percutaneously, the need to inject it through a relatively narrow needle or cannula also greatly increases the need for a high pressure driver. Still further, implantation of PMMA into a relatively closed implantation site (e.g., trabecular bone) further increases the resistance to flow of the PMMA, at the same time increasing the pressure requirements of the driver. Thus, a high pressure applicator that has enough storage capacity to perform a complete implantation procedure without having to reload the device in the midst of the procedure, and which is consistently controllable, for an even, constant application of pressure during delivery of the entirety of the implant material is preferred.
Attempts have been made to increase the ability to apply pressure to drive PMMA to the vertebral implant site by providing a smaller barrel syringe, but this holds less volume and must be refilled once or several times to deliver enough volume of PMMA to the site. Since there is a limited amount of time to work with PMMA before it begins to polymerize or set up, this type of procedure is more difficult to successfully complete within the allotted time, and thus poses an additional risk to the success of the operation. An improved high pressure applicator disclosed in U.S. application Ser. No. 09/053,108, has been developed for controllably applying higher pressures to a source of hard tissue implant material to successfully implant the material at the desired location in a single batch, for the performance of hard tissue implantation and particularly for percutaneous vertebroplasty. U.S. application Ser. No. 09/053,108 is hereby incorporated by reference in its entirety.
Leakage or seepage of PMMA from the vertebral implant site can cause a host of complications some of which can be very serious and even result in death. For example, Weil et al. reported cases of sciatica and difficulty in swallowing which were related to focal cement leakage, Radiology 1996;Vol 199, No. 1,241-247. A leak toward the distal veins poses an even more serious risk, since this can cause a pulmonary embolism which is often fatal. In addition to misplacement of the cannula away from the intended implant site, leakage or seepage also may occur even when the cannula is properly placed. For example, overfilling of the intended implant site, under pressure, can result in seepage or leakage after removal of the cannula from the implant site.
Overfilling can occur simply by injecting a larger volume of implant material than the void to be filled at the implant site. Additionally, due to the high pressures involved in the implant procedure, compliance within the delivery system can act as a capacitance under pressure, thereby storing a volume of the implant material and energy under pressure. Upon release of the pressure at the pressure applicator end, the compliant portion of the system also releases its energy and consequently drives an additional amount of implant material into the implant site, thereby overfilling the intended implant site. Upon removal of the delivery system, a leakage or seepage problem ensues at the implant site as a result of the overfilling.
In a known arrangement disclosed by Tronzo in U.S. Pat. No. 4,653,489, a fenestrated hollow hip screw is adapted for delivery of bone cement to an osteoporitic hip fracture site in a femur. The screw is permanently fixed to the femur by screwing it thereto. Once the screw is mechanically fixed to the femur, bone cement is injected into the site by a 20 cc syringe through a standard intravenous (IV) extension tube which connects with a cannulation in the screw. In this situation, the cannulation is large and therefor a relatively lower driving pressure is required for delivery of the bone cement as compared to the situations described above. Additionally, the fact that the screw stays in place even after the injection of the bone cement helps to lessen the occurrence of seepage or leakage.
Nevertheless, compliance of the IV tubing allows the tubing walls to expand upon initial application of pressure by the syringe, thereby decreasing the response performance of the arrangement. That is, the walls of the tubing expand, thereby storing a certain amount of bone cement therein, before the bone cement moves forward and into the implantation site. Additionally, the relative elasticity of the tubing walls stores energy upon expansion thereof Consequently, when an operator first applies a driving force to the plunger of the syringe to establish a driving pressure to drive the bone cement, immediate flow of the cement to the implantation site does not occur. Rather, the walls of the tubing first stretch and act as a reservoir of the bone cement, and flow does not begin until a threshold pressure required to cause flow of the cement is reached and until no further expansion of the tubing walls occurs. This thereby reduces the response performance of the system.
Additionally, after flow has begun and the decision is made by the operator to stop the flow to the implant site, the operator removes all application of pressure to the bone cement by removing any application of force to the plunger. At this time, the stored energy in the expanded walls is released, thereby returning the IV tube to its pre-pressurization configuration and dimension and driving an additional amount of bone cement through the IV tube and into the implantation site. This additional amount of flow is sometimes referred to as xe2x80x9coozingxe2x80x9d or xe2x80x9cdripxe2x80x9d.
Malcolm et al. in U.S. Pat. No. 4,274,163 discloses a prosthetic fixation technique in which pressurized bone cement is injected through a prosthesis and into an implantation site. Although a flexible inlet tubing 24 is used to deliver pressurized cement to the prosthesis, compliance of the tubing is not a concern, since Malcom et al. expects leakage or seepage of the bone cement. Exit cannulae 72 and 74 are provided in the prosthesis through which blood and other bodily fluids are forced out of the implantation site by the introduction of the pressurized cement. Upon observation of a flow of bone cement out of the exit cannulae, the operator knows to stop injecting bone cement. Thus, any oozing or drip upon cessation of the driving pressure is easily accommodated by the exit cannulae.
Dozier, Jr. discloses an injector for directly injecting bone cement into a bone cavity in U.S. Pat. No. 4,815,454. The injector used is an injection gun similar to a caulking gun. The nozzle of the cement cartridge held by the injection gun is inserted into a tapered bore of an expander member and compliant plug which is located in the opening to the implant site. In this situation, a relatively large volume of bone cement is placed and the emphasis of the setup is an application of sufficient pressure to drive the cement into the trabeculae in the implant site.
High pressure extension lines are commercially available, with pressure ratings of up to 1200 psi. These lines are made from materials such as braided polyurethane, braided PVC or PVC tubing. Although capable of withstanding pressures up to about 1200 psi, these lines are compliant and exhibit the same xe2x80x9coozingxe2x80x9d or overfilling phenomenon as discussed above, due to the storage of implant material in the expanded volume of the lines under pressure. As shown in FIG. 10, the high pressure extension line 150 radially expands (shown exaggerated in phantom lines) upon application of pressure by the syringe 160 (force F applied to plunger 162), thereby decreasing the response performance of the arrangement. That is, the walls of the tubing 150 expand, thereby acting as a reservoir, storing a certain amount of implant material therein, before the implant material flows forward into the implantation site, and maintains that storage as long as the pressure is maintained.
Consequently, when an operator first applies a driving force F to the plunger 162 of the syringe 160 to establish a driving pressure to drive the implant material, immediate flow of the implant material to the implantation site does not occur. Rather, the walls of the line 150 first stretch and act as a reservoir storing the implant material, and flow does not begin until a threshold pressure required to cause flow of the implant material is reached and until no further expansion of the tubing walls occurs. This thereby reduces the response performance of the system.
After flow has begun into the implant site, the operator monitors the filling of the site. When it is observed that the site has been substantially filled, and the decision is made by the operator to stop the flow to the implant site, the operator removes all application of pressure to the implant material by removing any application of force F to the plunger 162. At this time, the stored energy in the expanded walls is released, and the elasticity of the high pressure line 150 returns it to its pre-pressurization configuration and dimension, shown in FIG. 11. Since the system is closed at the end of the line 150 connected to the syringe 160, the contraction of the line 150 drives an additional volume of the implant material to the open end of the system, i.e., the opening 182 at the end of cannula 180, which often leads to overfilling.
Thus, there exists a need for an improved system and procedure for controllably applying higher pressures to a source of implant material to successfully and accurately implant a volume of the material at the desired location in a single batch, while at the same time enables both the applicator, and thus the user""s hand to be distanced from the radiographic field or other viewing field. In particular there is a need for an improved system for the performance of percutaneous vertebroplasty.
The present invention includes a substantially non-compliant conduit for delivering implant material under high pressure, from a pressure source to a device which delivers the material to an implant site. The conduit preferably comprises a substantially non-compliant tube having first and second ends, which are adapted to be removably fixed to the pressure source and the device, respectively.
The conduit preferably has a burst pressure at least 2,000 psi , more preferably at least about 2,500 psi and up to at least about 4,000 psi. The conduit may or may not have a reinforcing structure. In the embodiments employing a reinforcing structure, the reinforcing structure is preferably a non-stretch coil within a wall of the conduit. The coil is preferably formed of flat wire, but may also be formed of round wire. Alternatively, the reinforcement may be a braided structure.
Further disclosed is a substantially non-compliant system for percutaneously delivering implant material, which includes a delivery port providing percutaneous access to an implant site; a high pressure applicator for driving the delivery of the implant material; and a substantially non-compliant tube interconnecting said high pressure applicator and said delivery port. A preferred example of a device providing the delivery port is a cannula, but other devices, such as needles may also be employed.
A system for delivering implant material, either percutaneously or otherwise, is disclosed to include a substantially non-compliant delivery device providing access to an implant site; a high pressure applicator for driving the delivery of the implant material; and a substantially non-compliant conduit adapted to interconnect said high pressure applicator and said delivery device.
A method of delivering implant material is also described, in which a substantially non-compliant delivery device is inserted into a tissue site where implantation of an implant material is desired. Next, a substantially non-compliant, high pressure conduit is connected to an input port of the delivery device, and to a high pressure applicator containing a predetermined volume of tissue implant material. After connection of the system a high pressure is applied to the implant material, via the high pressure applicator, to drive the implant material through the conduit and the device and into the site.